1. Field of the Invention
The present invention relates to a glazed metal film resistor device provided with a thick film resistor on an insulative ceramic base body such as alumina, and the thick film resistor is formed by coating a surface of the base body with a thick film resistor paste and firing.
2. Description of the Related Art
The glazed metal film resistor is a resistor, whose size is small and whose resistance value can be manufactured to a high resistance value region. The resistor is very stable against severe environments and overloads, and the resistor is widely used in various electronic equipments. The glazed metal film resistor is manufactured, for example, by coating a surface of a columnar insulator such as alumina with a thick film resistor paste and firing the paste to form a thick film resistor of ruthenium oxide as primary component on the surface of the columnar insulator (Japanese laid-open patent publication 6-310302).
The thick film resistor comprises, for example, ruthenium oxide (RuO2) and glass, and it is known that as glass element increases, then resistance value of the thick film resistor becomes higher, and TCR value of the thick film resistor shifts to minus direction. Because of this fact, there is a problem that when the thick film resistor is formed on an insulator containing glass, the thick film resistor becomes to be affected by glass contained in the insulator, and the TCR value of the thick film resistor shifts to worse value from the original TCR value of the thick film resistor material (RuO2) itself. Also, an amount of glass contained in the base body (insulator) is not always equal. Therefore, since effects of glass contained in the insulator to the thick film resistor differs by every base body (insulator), then it is quite difficult to form equal characteristics among resistor devices, which are manufactured by the same process. Also, since resistance value of the resistor is expected to be higher from the resistance value of the thick film resistor material (RuO2) itself, then it is required to use more metal material than usual thick film resistor material.
The problem can be solved by using an insulator as a base body, which does not contain glass, however the insulator, which does not contain glass, is much expensive comparing to the insulator containing glass, and becomes a factor of cost increasing of the glazed metal film resistor device.